The principal objective of these studies is to characterize some of the proteins that are involved in mediating the actions of cAMP and glucocorticoid in tyrosine aminotransferase (TAT) synthesis in order to understand mechanisms by which cAMP and steroid hormone regulates specific functions in eukaryotic cells. The approach here is to study the biochemical processes that are affected by cAMP and by steroid hormone; to isolate proteins that are involved in the regulation of specific functions by cAMP and steroid hormone. Part I of this proposal is an analysis of the involvement of cAMP-dependent protein kinase in TAT induction. Protein kinase of various subcellular origin in rat liver will be studied using the photoaffinity labeling analogue of cAMP: 8-azido-cAMP. Appropriate cellular models will be used to demonstrate the causal relationship of cAMP-dependent protein phosphorylation and the regulation of TAT synthesis by cAMP. In part II of this proposal, I plan to continue my investigation on regulation of protein phosphorylation by steroid hormone. The regulatory subunit of Type II cAMP-dependent protein kinase can exist in a phospho- and dephospho-form. Phosphorylation of this protein is capable of regulating kinase activity. cAMP and in vivo administration of steroid hormone are capable of regulating the phosphorylation of this protein. This protein designated SCARP (Steroid and Cyclic AMP Regulated Phosphoprotein) will be characterized and purified in an effort to understand the precise mechanism by which steroid hormone regulates the phosphorylation of this protein. The difference of SCARP in steroid-treated and control liver will be studied utilizing the techniques of protein chemistry and immunology. The possible involvement of steroid-induced alteration in SCARP phosphorylation in the mechanism by which glucocorticoid regulates TAT synthesis will be studied, using steroid-resistant hepatoma cell variants. The goal is to utilize this system to begin to understand some of the biochemical processes that are affected both by cAMP and by steroid hormone. It is possible that these processes could be the basis for many of the well known synergistic and permissive actions of steroid hormone and cAMP.